1. Field of the Invention
The present invention relates to mounting technique of semiconductor elements on a semiconductor insulating circuit board, more particularly to a high-density semiconductor device characterized by a structure having a plurality of stacked semiconductor elements for coping with downsizing, elevating performance, and diversifying functions.
2. Background Art
FIG. 8 is a sectional view showing a conventional semiconductor device having semiconductor elements of different sizes stacked on an insulating circuit board. In the conventional stacked semiconductor device, as FIG. 8 shows, semiconductor elements 10 and 20 are mounted facing up on a circuit board 1, and element electrodes 11 and 21 are connected to a board electrodes 4b on the top surface of the circuit board 1 with wires 12 and 22, respectively. External electrodes 3 are provided on the under side surface of the circuit board 1, and the upper side of the circuit board 1 is encapsulated by an encapsulating resin 6b. 
Thus, the conventional semiconductor device having semiconductor elements 10 and 20 of different sizes stacked on an insulating circuit board 1 has the structure in which the upper semiconductor element 20 is smaller than the lower semiconductor element 10, and the element electrodes (chip electrodes) 11, 21 of such semiconductor elements 10, 20 are connected to board electrodes 4b using a wire bonding technique or the like. However, semiconductor elements of the same size cannot be stacked using such techniques. Also, for semiconductor elements having electrodes provided in the central portion of the elements, such techniques require long wires to connect these electrodes to the board electrodes, lowering the electrical properties.
The object of the present invention is to solve the above described problems in conventional semiconductor devices, and to provide a semiconductor device which enables higher density by stacking semiconductor elements of substantially the same size, and shorter loop length for internal connection.
According to one aspect of the present invention, a semiconductor device comprises a circuit board and a plurality of semiconductor elements. The circuit board has a top surface and a back surface on which board electrodes are arranged on said top and back surfaces, and in the circuit board predetermined openings are formed. Each of a plurality of semiconductor elements has a top surface and a back surface, and the element electrodes are arranged on said top surface. Further, a first semiconductor element is placed so that the top surface thereof faces to the top surface of said circuit board, and the element electrodes thereof are connected to the board electrodes on the back surface of said circuit board through said openings of said circuit board. A second semiconductor element is stacked so that the back surface thereof is joined to the back surface of said first semiconductor element, and the element electrodes thereof are connected to the board electrodes on the top surface of said circuit board.
According to another aspect of the present invention, a semiconductor device comprises a circuit board and a plurality of semiconductor elements. The circuit board has a top surface and a back surface, and the board electrodes are arranged on said top and back surfaces, and predetermined openings are formed in the circuit board. Each of a plurality of semiconductor elements has a top surface and a back surface, and element electrodes are arranged on said top surface. Further, a first semiconductor element is placed so that the top surface thereof faces to the top surface of said circuit board, and the element electrodes thereof are connected to the board electrodes on the back surface of said circuit board through said openings of said circuit board. A second semiconductor element having dimensions larger than the dimensions of said first semiconductor element is stacked such that the top surface thereof faces to the back surface of said first semiconductor element and the element electrodes thereof are out of the back surface of said first semiconductor element, and said element electrodes are connected to the board electrode on the back surface of said circuit board through said opening of said circuit board.
According to another aspect of the present invention, a semiconductor device comprises a circuit board and a semiconductor element. The circuit board has board electrodes placed on the top and back surfaces thereof and has a predetermined opening formed therein. The semiconductor element has element electrodes placed on the top surface thereof. The semiconductor element is placed so that the element electrodes thereof face to the top surface of said circuit board, and said element electrodes are connected to the board electrodes placed on the back surface of said circuit board through said opening formed in said circuit board. Further, said opening in said circuit board is formed to have a predetermined shape corresponding to the arrangement of element electrodes of said semiconductor element.
Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings.